Method and apparatus for detecting potentially dangerous conditions in a well bore during trips of the well string in and out of the well bore

ABSTRACT

A method and apparatus for detecting potentially dangerous conditions in a well bore which is being drilled by the use of a drill string suspended in the well bore and with a drilling mud system. The method and apparatus is arranged for detecting losses of drilling mud to the well bore formation and the incursion of well fluids into the well bore during times when the drill string is being run into and taken out of the well bore. The apparatus includes means for sensing the weight of the drill string suspended in the well bore during running in and coming out as an indication of the volume of space in the well bore occupied by the suspended drill string. Signal means are connected to the weight sensing means for generating a first signal representative of the drill string volume. Means are also provided for sensing the volume of drilling mud in the drilling mud system outside of the well bore during running in and coming out of operations. Signal means are also connected to the mud volume sensing means for generating a second signal representative of the aforesaid mud volume outside the well bore, and variations therein. Readout means, which may include a two-pen chart or the like, are connected to receive the first and second signals and for reading out variations between the two signals as either a loss of drilling mud to the formation or the incursion of fluid from the formation into the well bore.

United States Patent 1 Dower Dec. 31, 1974 METHOD AND APPARATUS FORDETECTING POTENTIALLY DANGEROUS CONDITIONS IN A WELL BORE DURING TRIPSOF THE WELL STRING IN AND OUT OF THE WELL BORE Ethell J. Dower, Houston,Tex.

[73] Assignee: Warren Automatic Tool Company,

Houston, Tex.

[22] Filed: Mar. 22, 1973 [21] Appl. No.: 343,787

[75] Inventor:

Primary Examiner-Jerry W. Myracle Attorney, Agent, or FirmLee R. Larkin[57] ABSTRACT A method and apparatus for detecting potentially dan- L/NETENS/ON TRANSMITTER BIAS RELAY SUPPL Y DEAD LINE CABLE 72 MUD LEV BIASRELAY TRANSMITTER 42 33 40 SUPPLY 30 MUD TANK ADJUSTABLE GAIN RELAY Z7SUPPLY gerous conditions in a well bore which is being drilled by theuse of a drill string suspended in the well bore and with a drilling mudsystem. The method and apparatus is arranged for detecting losses ofdrilling mud to the well bore formation and the incursion of well fluidsinto the well bore during times when the drill string is being run intoand taken out of the well bore. The apparatus includes means for sensingthe weight of the drill string suspended in the well bore during runningin and coming out as an indication of the volume of space in the wellbore occupied by the suspended drill string. Signal means are connectedto the weight sensing means for generating a first signal representativeof the drill string volume. Means are also provided for sensing thevolume of drilling mud in the drilling mud system outside of the wellbore during running in and coming out of operations. Signal means arealso connected to the mud volume sensing means for generating a secondsignal representative of the aforesaid mud volume outside the well bore,and variations therein. Readout means, which may include a two-pen chartor the like, are connected to receive the first and second signals andfor reading out variations between the two signals as either a loss ofdrilling mud to the formation or the incursion of fluid from theformation into the well bore.

10 Claims, 1 Drawing Figure CAPACITY TANK SUPPLY 20 BLEED OFF TWO PENRECORDER MUD ADJUSTABL VOLUME 44 ERELAY SIGNAL METHOD AND APPARATUS FORDETECTING POTENTIALLY DANGEROUS CONDITIONS IN A WELL BORE DURING TRIPSOF THE WELL STRING IN AND OUT OF THE WELL BORE BACKGROUND OF THEINVENTION a. Field of the Invention This invention relates to anapparatus and-method for detecting potentially dangerous conditions,such as potential blow-out conditions, which might arise during timeswhen the drill string is either being run into or removed from a wellbore, as for example, an oil well being drilled.

b. Description of the Prior Art As is common knowledge to those familiarwith the oil industry, fluid pressure in subterranean formationsgenerally increases with depth. If the fluid pressures are not properlycontrolled, then a potential blow-out condition may arise. Thispotentialblow-out condition is generally countered by the use of adrilling mud of the desired specific gravity, such that the hydrostaticpressure of the column'of drilling mud opposes the pressure of theformation fluid. In the event that the pressure of the hydrostaticcolumn of fluid is too little, then formation fluids such as gas, or thelike, may incur into the well bore and rise to the top, thereby creatinga blowout condition, with its known destructive propensities.Alternatively, if the weight of the column of mud is too great, thenthere is likely to be loss of the drilling mud to the formation, whichlikewise can result in undesirable and potentially dangerous conditions,as is well known to those skilled in the art.

During normal drilling operations, that is to say, when the drill stringis bottomed on the bottom of the well bore and is being rotated, anddrilling fluid is being circulated through the drill pipe, apparatushave been developed for sensing any changes in the volume of drillingmud in the drilling mud system, as indication of the potential blow-outconditions. One such device is marketed under the brand nameBARREL-O-GRAF by Warren Automatic Tool Company of Houston, Texas.However, this system has limited usefulness for detecting the aforesaidpotentially dangerous blow-out condition during times when the drillstring is either being run into or removed from the well bore. As iswell known to those skilled in the art, during times when the drillstring is being run into the well bore, drilling mud is displaced fromthe well bore and, conversely, when the drill string is being removedfrom the well bore, the level of drilling mud in the well bore declines,and thus additional mudmust be pumped thereinto in order to maintain theproper hydrostatic pressure. Because of this dynamic situation, there isneed for some apparatus and method which will be useful for detectingany potentially dangerout conditions that may arise during the aforesaidtripping operations.

In the past, it has been common practice for the drilling crew to pullone or more stands of drill pipe, and thereafter fill up the well boreby actuating the mud pump and counting the number of pump strokesrequired to fill up the well bore. The number of strokes of the pump isused to calculate the volume of mud used to fill up the well bore, whichfigure is then mentally compared with the theoretical or calculatedrequired displacement of the number of stands of drill pipe removed fromthe well bore. However, this system is very inaccurate and subject tooperational error. Many drill strings contain two or more sizes of drillpipe, in addition to the large drill collars, and such a system issubject to several sources of human and measurement error.

It is therefore an object of this invention to provide an improvedapparatus and method for detecting losses of drilling mud to the wellbore formation and the incursions of formation fluid into the well boreduring times when the drill string is being either run into or taken outof the well bore.

SUMMARY OF THE INVENTION Briefly stated, the method of this invention isarranged for detecting potentially dangerous conditions in a well borewhich is being drilled by the use of a drill string suspended in thewell bore and with a drilling mud system. The method is arranged fordetecting losses of drilling mud to the well bore formation and theincursion of formation fluids into the well bore during times when thedrill string is being run into and taken out of the well bore. Themethod includes the steps of sensing the weight of the drill stringsuspended in the well bore during the running in and coming outoperation as an indication of the volume of space in the well boreoccupied by the drill string. A first signal is generated which isrepresentative of the suspended drill string volume. The method alsoincludes sensing the volume of the drilling mud in the drilling mudsystem outside of the well bore during the running in and coming outoperation. A second signal is generated representative of the mud volumechange outside of the well bore.- The method includes monitoringvariations in the difference between the first and second signals asindications of loss of drilling mud to the formation and the incursionof fluids from the formation. Preferably, the well bore and the drillstring are maintained full of drilling mud during the sensing andmonitoring steps. It is to be understood that this maintaining of thewell bore full of mud can be done either continuously or periodically.It is to be also understood that the mud system can be either the usualmud system, or it can be a special fill up mud tank specially adaptedfor that purpose and which is connected to a pump which continuouslypumps drilling fluid to the well bore, from which it returns through anoverflow pipe, such that the well bore can continuously be maintained ina full condition.

The apparatus in this invention includes means for sensing the weight ofthe drill string suspended in the well bore during the running in andcoming out operation as an indication of the volume of space in the wellbore occupied by the drill string. Means are connected to the weightsensing means for generating a first signal representative of the drillstring volume. Means are also provided for sensing the volume of thedrilling mud in the drilling mud system outside the well bore during therunning in and coming out operations. Means are also provided forsensing changes in the volume of the drilling mud in the drilling mudsystem outside the well bore during the running in and coming outoperations. Means are connected to the mud volume sensing means forgenerating a second signal representative of the mud volume outside thewell bore. Read-out means are connected to receive the first and secondsignals for reading out variations therebetween as indications of lossof drilling mud to the formation or the incursion of drilling fluid fromthe formation into the well bore.

Preferably, calibration means are provided for setting the signals tocomparable volume scales. The read-out means may include recording meansfor displaying the signals on a chart, or the like, or may include meansfor generating a third signal which can actuate some alarm system, orthe like.

BRIEF DESCRIPTION OF THE DRAWINGS The Drawing is a schematic blockdiagram generally showing the arrangement of one form of the apparatusof this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT It is to be understood that theapparatus and. method of this invention are adaptable for use whendrilling a well bore such as an oil well utilizing a drill string suchmay be equipped with a pump 31 which is arranged to continuously drawmud from mud tank 30 and deliver it through fill-up line 32, whichterminates at the casing head, which connection will be normally belowthe northe well bore full of mud. As the drill string is withas a rotarydrill string suspended in a well bore and with i the drill string havinga drill bit on the lower end thereof. It is also contemplated that thedrilling system will include a mud system which includes means forcirculating a drilling mud through the drill pipe and across the bottomof the well bore to flush out cuttings and the like and to maintain thedesired hydrostatic pressure on the formation fluid.

The apparatus of this invention includes means for sensing the weight ofthe drill string suspended in the well bore during the running in andcoming out of the drill string as an indication of the volume of spacein the well bore occupied by the drill string. One convenient'means fordetecting the weight of the suspended drill string is to attach aconventional line tension transmitter such as pneumatic transmitter 11to the dead line cable 12, which is connected to the travelling block asis well known to those skilled in the art. Hence, the greater the weightof the suspended drill string, the greater will be the tension on deadline cable 12, and hence the signal produced by transmitter 11 on signalline '13 is proportional to the weight of the suspended drill string.Because of the known density of the drill string, it is therefore'knownthat the volume of mud displaced by the drill string is generallydirectly proportional to such weight. The pneumatic signal along signalline 13 is applied to a bias relay 14 through snubber 15, which dampensout undesirable fluctuations in the signal. The output of bias relay 14is applied to an adjustable pneumatic relay 16, which in turn applies apneumatic signal on signal line 17, which is connected through checkvalve 18 to one pen of a two-pen recorder 20, or, alternatively, otherappropriate read-out means.

Signal line l7,'downstream of check valve 18, may have attached theretoacapacity tank 21 and a bleedoff valve 22 for manipulating operation ofthe: system. Hence, the foregoing system generally provides the pipevolume signal to recorder 20. By manipulation of bias relay [4' andadjustable relay 16, the appropriate pen of recorder can be calibratedto record over the desired volume range.

The means for sensing the volume of drilling mud in the drilling mudsystem outside the well bore during running in and coming out of thedrill pipe, may be the conventional drilling mud tanks or may be aspecial fillup mud tank such as fill-up mud tank 30. Preferably mud tank30 is a separate fill-up tank of a known capacity such as 100 barrelsand is used to maintain the well bore full as the drill pipe is pulled.Hence, tank 30 drawn, the volume of mud in fill-up tank 30 willdecrease. Likewise, during such coming out operation, the weight of thedrill string and hence the volume of the drill string suspended in thewell bore decreases. Under usual circumstances, when there is no loss ofdrilling fluid to the formation or incursion of formation fluid into thewell bore, then changes of pipe volume suspended in the well bore willbe proportional to the I changes of mud volume in mud tank 30.

Hence, means are provided for sensing the volume of the drilling mud inthe drilling mud system outside the well bore which can convenientlytake the form of mud level pneumatic transmitter 40, which is arrangedto sense the level of mud in mud tank 30 and transmit a signal on signalline 41 which is representative of the volume of mud in mud tank 30.Line 41 is connected to an appropriate pneumatic bias relay 42. Theoutput of bias relay 42 is applied to adjustable relay 44 which likewiseapplies a pneumatic ou'tputon mud volume signal line 45, which connectsto the other pen of twopen recorder 20. By adjusting bias relay 42 andadjustment relay 44, the signal on signal line 45 can be adjusted suchthat the appropriate pen of two-pen recorder 20 can be adjusted tosubstantially the same volume scale as the other pen connected toreceive the pipe volume signal. It is to be understood that recorder 20may be a circular time chart, for example, having pens which areconnected as aforesaid and which provide a visible readout of the twosignals.

As stated before, the two signals, when properly calibrated and duringthe running in and coming out opera- 7 tions, will be recordingapproximately the same volume changes. In the event that there are anyvariations between the two signals above the normal level, then thiswould be indicative of a potentially dangerous condition. An increase ofdrilling fluid relative to pipe voltime which would indicate anincursion of drilling fluid into the formation. Conversely, in the eventthat the volume of mud relative to the volume of pipe suspended in thewell bore decreased, then this would indicate a loss of drilling fluidto the formation. Either one of these conditions can cause a potentialblow-out condition, and the well driller needs to be aware of suchconditions so that corrective actions can be taken.

It is to be understood that other types of weight sensing means can beused for sensing the weight of the suspended drill pipe, as for examplea load cell supported under the rotary table to measure the weight ofthe pipe when it is set'in the slips in the rotary table when the standis removed, or before the stand is added. It is to be understood thatthe signals generated may be either electrical or pneumatic, but theoperation thereof would be thesame. Other readout means can be used thana recorder. For example, the pipe volume signal and the mud volumesignal may be used to generate a third signal which is connected to anappropriate alarm system, for example, either audio or visual.

It is also to be understood that rather than using a special fill-up mudtank such as mud tank 30, the signal on line 31 can be taken from theconventional mud still have drilling fluid therein, a slug'of heaviermud may be introduced into the top of the drill pipe prior to pullingthe same, or trip mud of slightly lower density than drilling mud, maybe used. It is to be understood that the trip mud should be of the sametype as the drilling mud but slightly cut back with water.

It will thus be observed that this invention provides a method andapparatus for detecting potential blowout conditions which might ariseduring times when making trips with the drill stem either into or out ofthe well bore and eliminates the mental calculations heretofore utilizedin some instances and gives a positive readout at all times.-

As previously stated, the well bore may be maintained full of drillingmud during the sensing and monitoring steps, which maintaining may bedone periodically or continuously. However, it is preferable that thewell bore be full when the monitoring step is performed to provideaccurate measurements of mud volume.

Moreover, it is preferable to have the signals calibrated so that theymay be more easily compared in terms of volume. By recording thesignals, a permanent record may be made which may be useful in analyzingwell conditions at a subsequent time. Alternatively, the two generatedsignals may be used to generate a third signal, which in turn may beused to operate a single pen of a recorder or an audible alarm signal,or the like.

Further modification and alternative embodiments of the apparatus andmethod of this invention will be apparent to those skilled in the art inview of this description. Accordingly, this description is to beconstrued as illustrative only and is for the purpose of teaching thoseskilled in the art the manner of carrying out the invention. It is to beunderstood that the forms of the invention herewith shown and describedis to be taken as the presently preferred embodiment. Various changesmay be made in the shape, size and arrangement of parts. For example,equivalent elements or materials may be substituted for thoseillustrated and described herein, parts may be reversed, and certainfeatures of the invention maybe utilized independently of the use ofother features, all as would be apparent to one skilled in the art afterhaving the benefit of this description of the invention.

What is claimed is:

1. In a method of detecting potentially dangerous conditions in a wellbore which is being drilled by the use of a drill string suspended insaid well bore and with a drilling mud system, which method is arrangedfor detecting losses of drilling mud to the well bore formation and theincursion of fluid into the well bore from the formation during timeswhen the drill string is being run into and taken out of the well bore,the combination of steps comprising:

sensing the weight of the drill string suspended in said well boreduring said running in and coming out as an indication of the volume ofspace in said well bore occupied by said drill string;

generating a first signal representative of said suspended drill stringvolume;

sensing the volume of drilling mud in said drilling mud system outsideof said well bore during said running in and coming out operations;

generating a second signal representative of said mud volume outsidesaid well bore;

and monitoring variations in the difference between said first andsecond signals as indications of loss of drilling mud to the formationand the incursion of fluid from the formation.

2. The invention as claimed in claim 1 including:

maintaining said well bore and said drill string full of drilling mudduring said sensing and monitoring steps.

3. The invention as claimed in claim 1 including:

calibrating said first and second signals to comparable volume scales.

4. The invention as claimed in claim 3 wherein:

said monitoring step includes recording said signals on a common displaychart.

5. The invention as claimed in claim 3 wherein:

said monitoring step includes generating a third signal representativeof said differences between said first and second signals.

6. ln apparatus for detecting losses of drilling mud to the well boreformation and the incursions of fluid into the well bore from theformation which is being drilled by the use of a drill string suspendedin said well bore and with a drilling mud system, which apparatus isarranged for such detecting during times when the drill string is beingrun into and taken out of the well bore, the combination comprising:

means for sensing the weight of the drill string suspended in said wellbore during said running in and coming out as an indication of thevolume of space in said well bore occupied by said drill string;

means connected to said weight sensing means for generating a firstsignal representative of said drill string volume;

means for sensing the change of volume of drilling mud in said drillingmud system outside said well bore during said running in and coming outoperations; I

means connected to said mud volume sensing means for generating a secondsignal representative of said mud volume;

' and readout means connected to receive said first and second signalsfor reading out variations therebetween as indications of 'loss ofdrilling mud to the formation and the incursion of fluid from theformation into saidwell bore.

7. The invention-as claimed in claim 6 including:

means for filling said well bore full of drilling fluid at determinedtimes. a

8. The invention as claimedin claim 6 including:

calibration means for adjusting said signals to comparable volumescales.

9. The invention as claimed in claim 6 wherein:

saidreadout means includes means for recording said tween said first andsecond signals;

signals on a display chart. and means connected to said third signalgenerating 10. The invention as claimed in'claim 6 wherein: means forproducing an alarm signal when said 1 said readout means includes meansfor generating a third signal increased beyond a determined level.

third signal representative of said differences be- 5 UNITED STATESPATENT OFFICE CERTIFICATE OF CORRECTION P n 3,857,281 Dated December 31,1974 Inventor(s) Ethell J. Dower It is certified that error appears inthe above-identified patent and that said Letters Patent are herebycorrected as shown below:

On the title page "METHOD AND APPARATUS FOR DETECTING POTENTIALLYDANGEROUS CONDITIONS IN A WELL BORE DURING TRIPS OF THE WELL STRING INAND OUT OF THE WELL BORE" should read METHOD AND APPARATUS FOR DETECTINGPOTENTIALLY DANGEROUS CONDITIONS IN A WELL BORE DURING TRIPS OF THEDRILL STRING IN AND OUT OF THE WELL BORE-- In column 1, line 3, "WELL"second occurrence should read DRILL Signed and sealed this 6th day ofMay 1.975.

(SEAL) Attest:

C. MARSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officerand Trademarks ORM PO-105O (10-69) USCOMM-DC 60378-1 69 i U.S.GOVERNMENT PRINTING OFFICE I908 Q-S66-33l.

1. In a method of detecting potentially dangerous conditions in a wellbore which is being drilled by the use of a drill string suspended insaid well bore and with a drilling mud system, which method is arrangedfor detecting losses of drilling mud to the well bore formation and theincursion of fluid into the well bore from the formation during timeswhen the drill string is being run into and taken out of the well bore,the combination of steps comprising: sensing the weight of the drillstring suspended in said well bore during said running in and coming outas an indication of the volume of space in said well bore occupied bysaid drill string; generating a first signal representative of saidsuspended drill string volume; sensing the volume of drilling mud insaid drilling mud system outside of said well bore during said runningin and coming out operations; generating a second signal representativeof said mud volume outside said well bore; and monitoring variations inthe difference between said first and second signals as indications ofloss of drilling mud to the formation and the incursion of fluid fromthe formation.
 2. The invention as claimed in claim 1 including:maintaining said well bore anD said drill string full of drilling mudduring said sensing and monitoring steps.
 3. The invention as claimed inclaim 1 including: calibrating said first and second signals tocomparable volume scales.
 4. The invention as claimed in claim 3wherein: said monitoring step includes recording said signals on acommon display chart.
 5. The invention as claimed in claim 3 wherein:said monitoring step includes generating a third signal representativeof said differences between said first and second signals.
 6. Inapparatus for detecting losses of drilling mud to the well boreformation and the incursions of fluid into the well bore from theformation which is being drilled by the use of a drill string suspendedin said well bore and with a drilling mud system, which apparatus isarranged for such detecting during times when the drill string is beingrun into and taken out of the well bore, the combination comprising:means for sensing the weight of the drill string suspended in said wellbore during said running in and coming out as an indication of thevolume of space in said well bore occupied by said drill string; meansconnected to said weight sensing means for generating a first signalrepresentative of said drill string volume; means for sensing the changeof volume of drilling mud in said drilling mud system outside said wellbore during said running in and coming out operations; means connectedto said mud volume sensing means for generating a second signalrepresentative of said mud volume; and readout means connected toreceive said first and second signals for reading out variationstherebetween as indications of loss of drilling mud to the formation andthe incursion of fluid from the formation into said well bore.
 7. Theinvention as claimed in claim 6 including: means for filling said wellbore full of drilling fluid at determined times.
 8. The invention asclaimed in claim 6 including: calibration means for adjusting saidsignals to comparable volume scales.
 9. The invention as claimed inclaim 6 wherein: said readout means includes means for recording saidsignals on a display chart.
 10. The invention as claimed in claim 6wherein: said readout means includes means for generating a third signalrepresentative of said differences between said first and secondsignals; and means connected to said third signal generating means forproducing an alarm signal when said third signal increased beyond adetermined level.